Near-Infrared Phosphorescent Supramolecular Alkyl/Aryl-Iridium Porphyrin Assemblies by Axial Coordination

Abstract

Five-coordinated d⁶ metal complexes are relatively uncommon but can be useful building blocks for the construction of supramolecular assemblies. In this work we have used the strong trans effect of aryl and alkyl ligands for the synthesis of luminescent five-coordinated organoiridium porphyrins, which are useful building blocks for the construction of metallamacrocycles and metallacages of iridium through metal-ligand interactions at the axial positions of iridium porphyrins (Ir(por)). Diverse di- or tritopic aryl or alkyl linkers were employed as the axial ligands to coordinate Ir(por) at an axial position to afford di- or trinuclear five-coordinated [{Ir(ttp)}_n (X)] (ttp=5,10,15,20-tetrakis(p-tolyl)porphyrinato(2-); n=2, X=diaryl; n=3, X=trialkyl). [{Ir(ttp)}_n (X)] could be further coordinated with ditopic isocyanide or pyridine ligands at the other axial site of each Ir(ttp) to give unprecedented cyclic supramolecular metalloporphyrin assemblies, including tetra- and hexanuclear metallamacrocycles and hexanuclear metallacages. The Ir(por) metallamacrocycles and metallacages display phosphorescence in the near-infrared region with quantum yields of around 2 % and microsecond emission lifetimes.

Keywords: N ligands; axial coordination; iridium; luminescence; porphyrinoids; supramolecular chemistry.